Bioturbation-driven release of organic contaminants from Baltic sea sediments mediated by the invading polychaete Marenzelleria neglecta

Baltic Sea sediments are among the world's most polluted regarding eutrophication and contamination. Eutrophication-induced hypoxia has caused deplebon of bioturbating macrofauna in vast areas, producing laminated sediments. We investigated if reoxygenation and colonization by the invading deep-burrowing polychaete Marenzelleria neglecta may cause an augmented contaminant release from Baltic Sea sediments. Intact laminated sediment cores were exposed either to in situ hypoxia, reoxygenation, or reoxygenation combined with bioturbating M. neglecta. The release fluxes of particle-associated (N-Part) and dissolved (N-Diss) PCBs and chlorinated pesticide residues (POPS) were quantified (GC-ECD) after 85 d along with contaminant concentrations in sediment and biota. Lavoisier-based mass transfer coefficients (K-f) were calculated from N-Diss. Sediment contaminant concentrations were high (Sigma PCB7: 42-52 ng g(sediment)(-1) dw) due to emissions from Stockholm. N-Diss always exceeded N-Part by an order of. magnitude. Bioturbation enhanced N-Diss and K-f from hypoxic sediments 0.7 - 3 times while reoxygenation alone had no significant effect. M. neglecta accumulated low amounts of contaminants but significantly stimulated aquatic release of bioavailable sequestered contaminants. Bioturbation should be included in aquatic contaminant fate models. We advise to consider quiescent pollutant sources and possible ecological shifts when aiming to restore eutrophicated aquatic environments.